U.S. patent number 10,389,178 [Application Number 15/339,262] was granted by the patent office on 2019-08-20 for method for controlling dc-ac converter and ground assembly and wireless power transfer method using the same.
This patent grant is currently assigned to Hyundai Motor Company. The grantee listed for this patent is HYUNDAI MOTOR COMPANY. Invention is credited to Gyu Yeong Choe, Woo Young Lee, Hyun Wook Seong.
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United States Patent |
10,389,178 |
Lee , et al. |
August 20, 2019 |
Method for controlling DC-AC converter and ground assembly and
wireless power transfer method using the same
Abstract
Disclosed are DC-to-AC converter control methods, ground
assemblies and wireless power transfer methods using the same. A
method for controlling a DC-to-AC converter of a ground assembly
used for wireless power transfer, which includes first, second,
third, and fourth switches arranged in a form of a bridge circuit
between a power source and a primary coil, may comprise detecting a
current flowing through the primary coil at a rising edge of an
output voltage signal of the DC-to-AC converter; determining
whether a strength of the current is at a negative level which
falls within a predetermined reference range; and in response to a
determination that the current is not at the negative level,
changing switching frequencies of the DC-to-AC converter.
Inventors: |
Lee; Woo Young (Yongin-si,
KR), Seong; Hyun Wook (Hwaseong-si, KR),
Choe; Gyu Yeong (Suwon-si, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
HYUNDAI MOTOR COMPANY |
Seoul |
N/A |
KR |
|
|
Assignee: |
Hyundai Motor Company (Seoul,
KR)
|
Family
ID: |
57206153 |
Appl.
No.: |
15/339,262 |
Filed: |
October 31, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170126062 A1 |
May 4, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Nov 2, 2015 [KR] |
|
|
10-2015-0153200 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M
3/158 (20130101); H02J 50/80 (20160201); B60L
53/122 (20190201); H02J 7/00034 (20200101); B60L
53/126 (20190201); H02J 50/10 (20160201); H02J
7/025 (20130101); H02J 50/12 (20160201); H02M
3/33523 (20130101); Y02T 90/127 (20130101); Y02T
90/122 (20130101); Y02T 90/12 (20130101); Y02T
90/14 (20130101); Y02T 10/7005 (20130101); Y02T
10/7072 (20130101); Y02T 10/70 (20130101) |
Current International
Class: |
H02J
50/10 (20160101); H02M 3/335 (20060101); B60L
53/12 (20190101); H02J 50/80 (20160101); H02J
7/02 (20160101); H02J 50/12 (20160101); H02M
3/158 (20060101) |
Field of
Search: |
;307/104 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chang; Joseph
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Claims
What is claimed is:
1. A method for controlling a direct current to alternating current
(DC-to-AC) converter of a ground assembly used for wireless power
transfer, which includes first, second, third, and fourth switches
arranged in a form of a bridge circuit between a power source and a
primary coil, the method comprising: detecting a first current
flowing through the primary coil at a rising edge of an output
voltage signal of the DC-to-AC converter and a second current
flowing through the primary coil at a falling edge of the output
voltage signal of the DC-to-AC converter, wherein the rising edge
corresponds to a time when the output voltage signal of the
DC-to-AC converter rises from 0V to a positive level, and the
falling edge corresponds to a time when the output voltage signal
of the DC-to-AC converter falls from 0V to a negative level;
decreasing a switching frequency of the DC-to-AC converter when the
first current has an excessive negative level lower than a first
reference level which is negative at the rising edge and the second
current has an excessive positive level higher than a second
reference level which is positive at the falling edge; and
increasing the switching frequency of the DC-to-AC converter when
the first current has a positive level at the rising edge.
2. A ground assembly comprising: a first power converting part
connected to a power source; a primary coil; a direct current to
alternating current (DC-to-AC) converter including first, second,
third, and fourth switches arranged in a form of a full bridge
circuit between the first power converting part and the primary
coil; a sensor connected to the primary coil and detecting a
current and a voltage of the primary coil; and a controller
connected to the sensor and controlling the DC-to-AC converter,
wherein the controller detects, via the sensor, a first current
flowing through the primary coil at a rising edge of an output
voltage signal of the DC-to-AC converter and a second current
flowing through the primary coil at a falling edge of the output
voltage signal of the DC-to-AC converter, and changes a switching
frequency of the DC-to-AC converter according to a level of the
first current or the second current, the rising edge corresponding
to a time when the output voltage signal of the DC-to-AC converter
rises from 0V to a positive level, and the falling edge
corresponding to a time when the output voltage signal of the
DC-to-AC converter falls from 0V to a negative level, wherein the
controller decreases the switching frequency of the DC-to-AC
converter, when the first current has an excessive negative level
lower than a first reference level which is negative at the rising
edge, and the second current has an excessive positive level higher
than a second reference level which is positive at the falling
edge, and wherein the controller increases the switching frequency
of the DC-to-AC converter when the first current has a positive
level at the rising edge.
3. The ground assembly according to claim 2, wherein the controller
comprises: a sensing part configured to detect a level of a voltage
or current sensed by the sensor; a comparison part configured to
compare the level of the current with zero or the first and second
reference levels; and an adjusting part configured to change the
switching frequency of the DC-to-AC converter according to a
comparison result of the comparison part.
4. The ground assembly according to claim 3, further comprising a
realignment part configured to realign the primary coil and a
secondary coil by moving the primary coil, the secondary coil, or
both according to a current output power level after the adjusting
part changes the switching frequency.
5. The ground assembly according to claim 2, wherein the DC-to-AC
converter is a phase-shifted full-bridge converter.
6. The ground assembly according to claim 5, wherein, in the
DC-to-AC converter, a first terminal of the first switch is
connected to a second terminal of the third switch, a second
terminal of the first switch and a first terminal of the third
switch are connected to both ends of the primary coil, a first
terminal of the fourth switch is connected to a second terminal of
the second switch, a second terminal of the fourth switch and a
first terminal of the second switch are connected to the both ends
of the primary coil, and a first connection node of the first and
third switches and a second connection node of the fourth and
second switches are connected to both output ends of the first
power converting part.
7. A wireless power transfer method performed in a controller of a
wireless power transfer system, the method comprising: detecting a
first current flowing through a primary coil at a rising edge of an
output voltage signal of a direct current to alternating current
(DC-to-AC) converter located between a power source and the primary
coil, wherein the rising edge corresponds to a time when the output
voltage signal of the DC-to-AC converter rises from 0V to a
positive level; detecting a second current flowing through the
primary coil at a falling edge of the output voltage signal of the
DC-to-AC converter, wherein the falling edge corresponds to a time
when the output voltage signal of the DC-to-AC converter falls from
0V to a negative level; decreasing a switching frequency of the
DC-to-AC converter when the first current has an excessive negative
level lower than a first reference level which is negative at the
rising edge and the second current has an excessive positive level
higher than a second reference level which is positive at the
falling edge; and increasing the switching frequency of the
DC-to-AC converter when the first current has a positive level at
the rising edge.
8. The method according to claim 7, further comprising: after the
changing, comparing a current output of the wireless power transfer
system with a reference output; and realigning the primary coil and
a secondary coil which inductively couples with the primary coil by
moving the primary coil, the secondary coil, or both according to a
comparison result in the comparing.
9. The method according to claim 7, wherein the controller includes
at least one of a ground assembly (GA) controller included in a GA
of the wireless power transfer system, a controller in the DC-to-AC
converter in the GA, and a vehicle assembly (VA) controller
connected with the GA controller via a wireless communication link.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to Korean Patent Application No.
2015-0153200 filed on Nov. 2, 2015 in the Korean Intellectual
Property Office (KIPO), the entire contents of which are hereby
incorporated by reference.
TECHNICAL FIELD
The present disclosure relates to a wireless power transfer system,
and more particularly, to a method for controlling a DC-to-AC
converter, a ground assembly using the same, and a wireless power
transfer method using the same.
BACKGROUND
Due to environmental pollution and oil energy depletion, world-wide
studies on environment-friendly electric vehicles (EV) are going
along. As demands for and developments on EVs and plug-in hybrid
vehicles (PHEV) increase, an on-board charger (OBC) for
high-voltage battery charging becomes an essential component in
automotive industry. Meanwhile, instead of conductive charging in
which connectors are used, wireless power transfer (WPT)
technologies used for charging high-voltage batteries without
connectors have been introduced.
In a wireless charging system for EV charging, a primary pad and a
secondary pad can be modeled as a transformer in an equivalent
circuit. As compared with conventional converter transformers, a
coupling coefficient is relatively low since an air-gap between the
primary pad and the secondary pad is very large. That is, since
magnetizing inductance is much larger than leakage inductance, it
may become difficult to transfer power to an output. Therefore, a
method, in which at least one capacitor is applied to the primary
pad and secondary pad so that a resonance between the pads is
caused by inductance and capacitance of the pads, is used
usually.
Usually, a phase-shifted full-bridge converter is used as a
converter for the wireless power transfer system, which is
connected to a front end of the primary pad. Also, a zero voltage
switching (ZVS) technique is used for improving efficiency of the
converter. It is not so difficult to design the converter to
achieve ZVS by using capacitances of the primary and secondary
pads.
However, misalignment between the primary and secondary pads,
manufacturing tolerances of the pads and capacitors, and different
characteristics of them may break their resonance during wireless
charging. Also, in this reason, inverse-currents flowing through
switches in the converter may be generated excessively, ZVS of the
converter may not be guaranteed, and efficiency of the wireless
power transfer system may degrade rapidly.
Also, switches having large current capacity should be used in
order to cope with the inverse-currents. In addition, if the ZVS is
not guaranteed, increase of electromagnetic interference (EMI)
caused by hard switching may demand an additional filter for
reducing the EMI, whereby the size and material cost of the total
system are increased.
SUMMARY
Accordingly, exemplary embodiments of the present disclosure are
provided to substantially obviate one or more problems due to
limitations and disadvantages of the related art.
Exemplary embodiments of the present disclosure provide a direct
current to alternating current (DC-to-AC) converter, which can
minimize inverse-currents flowing through switches and guarantee
ZVS even when misalignment between primary and secondary pads
and/or manufacturing tolerances of pads and capacitors exist in a
wireless power transfer system or a wireless charging system.
Exemplary embodiments of the present disclosure also provide a
ground assembly providing high efficiency and performance by using
the above-described -DC-to-AC converter.
Exemplary embodiments of the present disclosure also provide a
wireless power transfer method which can enhance stability and
reliability of wireless power transfer by using the DC-to-AC
converter.
In order to achieve the above-described objective, an aspect of the
present disclosure provides a method for controlling a direct
current to alternating current (-DC-to-AC) converter of a ground
assembly used for wireless power transfer, which includes first,
second, third, and fourth switches arranged in a form of a bridge
circuit between a power source and a primary coil. The method may
comprise detecting a current flowing through the primary coil at a
rising edge of an output voltage signal of the DC-to-AC converter;
determining whether the detected current is at a negative level
which falls within a predetermined reference range; and in response
to a determination that the current is not at the negative level
which falls within the predetermined reference range, changing
switching frequencies of the DC-to-AC converter.
Also, in the determining, it may be determined whether the detected
current is at an excessive negative level which does not fall
within the predetermined reference range.
Here, in response to a determination that the detected current is
at the excessive negative level, the switching frequencies of the
DC-to-AC converter may be decreased.
Here, in response to a determination that the detected current is
at a positive level, the switching frequencies of the DC-to-AC
converter may be increased.
Also, in the detecting, a first current flowing through the primary
coil may be detected at a first rising edge to a positive pule of
the output voltage signal, and a second current flowing through the
primary coil may be detected at a second rising edge to a negative
pulse of the output voltage signal.
Here, in the determining, it may be determined whether the second
current is at an excessive negative level which does not fall
within the predetermined reference range.
Also, in response to a determination that the second current is at
the excessive negative level, the switching frequencies of the
-DC-to-AC converter may be decreased.
In order to achieve the above-described objective, another aspect
of the present disclosure provides a ground assembly comprising a
first power converting part connected to a power source; a primary
coil; a direct current to alternating current (DC-to-AC) converter
including first, second, third, and fourth switches arranged in a
form of a full bridge circuit between the first power converting
part and the primary coil; a sensor connected to the primary coil
and detecting a current and a voltage of the primary coil; and a
controller connected to the sensor and controlling the DC-to-AC
converter. The controller detects, via the sensor, a first current
flowing through the primary coil at a first rising edge of an
output voltage signal of the DC-to-AC converter and a second
current flowing through the primary coil at a second rising edge of
the output voltage signal of the DC-to-AC converter, and changes
switching frequencies of the DC-to-AC converter according to a
level of the first current or the second current.
Also, the controller may decrease the switching frequencies of the
DC-to-AC converter, in response to a determination that the first
current has an excessive negative level lower than a first
reference level which is negative at the first rising edge, and the
second current has an excessive positive level higher than a second
reference level which is positive at the second rising edge.
Also, the controller may increase the switching frequencies of the
DC-to-AC converter in response to a determination that the first
current has a positive level at the first rising edge.
Also, the controller may comprise a sensing part configured to
detect a level of a voltage or current sensed by the sensor; a
comparison part configured to compare the level of the current with
zero or the first and second reference levels; and an adjusting
part configured to change switching frequencies of the DC-to-AC
converter according to a comparison result of the comparison
part.
Also, the ground assembly may further comprise a realignment part
configured to realign the primary coil and a secondary coil by
moving the primary coil, the secondary coil, or both according to a
current output power level after the adjusting part changes the
switching frequencies.
Also, the DC-to-AC converter may be a phase-shifted full-bridge
converter.
Also, in the DC-to-AC converter, a first terminal of the first
switch is connected to a second terminal of the third switch, a
second terminal of the first switch and a first terminal of the
third switch are connected to both ends of the primary coil, a
first terminal of the fourth switch is connected to a second
terminal of the second switch, a second terminal of the fourth
switch and a first terminal of the second switch are connected to
the both ends of the primary coil, and a first connection node of
the first and third switches and a second connection node of the
fourth and second switches are connected to both output ends of the
first power converting part.
In order to achieve the above-described objective, still another
aspect of the present disclosure provides a wireless power transfer
method performed in a controller of a wireless power transfer
system. The method may comprise detecting a first current flowing
through a primary coil at a first rising edge of an output voltage
signal of a direct current to alternating current (DC-to-AC)
converter located between a power source and the primary coil;
detecting a second current flowing through the primary coil at a
second rising edge of the output voltage signal of the DC-to-AC
converter; and changing switching frequencies of the DC-to-AC
converter according to a level of the first current or the second
current.
Also, in response to a determination that at the first rising edge,
the first current is at an excessive negative level lower than a
first reference level which is negative, the switching frequencies
of the DC-to-AC converter may be decreased.
Also, in response to a determination that at the second rising
edge, the second current is at an excessive positive level higher
than a second reference level which is positive, the switching
frequencies of the DC-to-AC converter may be decreased.
Also, in response to a determination that at the first rising edge,
the first current is at a positive level, the switching frequencies
of the DC-to-AC converter may be increased.
Also, the method may further comprise, after the changing,
comparing a current output of the wireless power transfer system
with a reference output; and realigning the primary coil and a
secondary coil which inductively couples with the primary coil by
moving the primary coil, the secondary coil, or both according to a
comparison result in the comparing.
Also, the controller may include at least one of a ground assembly
(GA) controller included in a GA of the wireless power transfer
system, a controller in the DC-to-AC converter in the GA, and a
vehicle assembly (VA) controller connected with the GA controller
via a wireless communication link.
According to the above-described DC-to-AC converter control method,
ground assembly, and wireless power transfer method, even when
misalignment between primary and secondary pads of a wireless
charging system or wireless power transfer system exists, or
manufacturing tolerances of the pads or capacitors used for the
pads exist, inverse currents flowing through switches can be
minimized, and zero voltage switching (ZVS) can be guaranteed.
Also, even when misalignment between the primary pad and the
secondary pad exists in forward/backward, left/right,
upward/downward, or their combinational direction, the efficiency
and output of the system may gradually degrade without rapid
degradation. In addition, during a time period obtained by
preventing the rapid degradation of the efficiency and output, the
pads can be realigned in accordance with determination on whether
the primary and secondary pads are properly aligned.
Also, as compared to the conventional structure having similar
performance (efficiency and output), the size and material cost of
the wireless power transfer system can be reduced.
BRIEF DESCRIPTION OF DRAWINGS
Exemplary embodiments of the present disclosure will become more
apparent by describing in detail exemplary embodiments of the
present disclosure with reference to the accompanying drawings, in
which:
FIG. 1 is a block diagram of a wireless power transfer system using
a DC-to-AC converter according to an exemplary embodiment of the
present disclosure;
FIG. 2 is a flow chart showing a DC-to-AC converter control method
according to an exemplary embodiment of the present disclosure;
FIG. 3 is a flow chart showing a DC-to-AC converter control method
according to another exemplary embodiment of the present
disclosure;
FIG. 4 is a block diagram of a wireless power transfer system which
can use a DC-to-AC converter control method according to
embodiments of the present disclosure;
FIG. 5 is a timing diagram of an optimal operation of a DC-to-AC
converter according to an exemplary embodiment of the present
disclosure;
FIG. 6 is a timing diagram of an operation of a DC-to-AC converter
according to a comparative example;
FIG. 7 is a timing diagram of an operation of a DC-to-AC converter
according to another comparative example;
FIG. 8 is a timing diagram of an operation of a DC-to-AC converter
according to an exemplary embodiment of the present disclosure;
FIG. 9 is a graph showing an advantage of a DC-to-AC converter
control method according to an exemplary embodiment of the present
disclosure;
FIG. 10 is a block diagram to explain a structure of a controller
which can be used in a ground assembly according to an exemplary
embodiment of the present disclosure; and
FIG. 11 is a flow chart showing a wireless power transfer method
using a ground assembly of FIG. 10.
DETAILED DESCRIPTION
Exemplary embodiments of the present disclosure are disclosed
herein. However, specific structural and functional details
disclosed herein are merely representative for purposes of
describing exemplary embodiments of the present disclosure,
however, exemplary embodiments of the present disclosure may be
embodied in many alternate forms and should not be construed as
limited to exemplary embodiments of the present disclosure set
forth herein. While describing the respective drawings, like
reference numerals designate like elements.
It will be understood that although the terms "first", "second",
etc. may be used herein to describe various components, these
components should not be limited by these terms. These terms are
used merely to distinguish one element from another. For example,
without departing from the scope of the present disclosure, a first
component may be designated as a second component, and similarly,
the second component may be designated as the first component. The
term "and/or" include any and all combinations of one of the
associated listed items.
It will be understood that when a component is referred to as being
"connected to" another component, it can be directly or indirectly
connected to the other component. That is, for example, intervening
components may be present. On the contrary, when a component is
referred to as being "directly connected to" another component, it
will be understood that there is no intervening components.
Terms are used herein only to describe the exemplary embodiments
but not to limit the present disclosure. Singular expressions,
unless defined otherwise in contexts, include plural expressions.
In the present specification, terms of "comprise" or "have" are
used to designate features, numbers, steps, operations, elements,
components or combinations thereof disclosed in the specification
as being present but not to exclude possibility of the existence or
the addition of one or more other features, numbers, steps,
operations, elements, components, or combinations thereof.
All terms including technical or scientific terms, unless being
defined otherwise, have the same meaning generally understood by a
person of ordinary skill in the art. It will be understood that
terms defined in dictionaries generally used are interpreted as
including meanings identical to contextual meanings of the related
art, unless definitely defined otherwise in the present
specification, are not interpreted as being ideal or excessively
formal meanings.
Terms used in the present disclosure are defined as follows.
`Electric Vehicle, EV`: An automobile, as defined in 49 CFR 523.3,
intended for highway use, powered by an electric motor that draws
current from an on-vehicle energy storage device, such as a
battery, which is rechargeable from an off-vehicle source, such as
residential or public electric service or an on-vehicle fuel
powered generator. The EV may be four or more wheeled vehicle
manufactured for use primarily on public streets, roads.
The EV may be referred to as an electric car, an electric
automobile, an electric road vehicle (ERV), a plug-in vehicle (PV),
a plug-in vehicle (xEV), etc., and the xEV may be classified into a
plug-in all-electric vehicle (BEV), a battery electric vehicle, a
plug-in electric vehicle (PEV), a hybrid electric vehicle (HEV), a
hybrid plug-in electric vehicle (HPEV), a plug-in hybrid electric
vehicle (PHEV), etc.
`Plug-in Electric Vehicle, PEV`: An Electric Vehicle that recharges
the on-vehicle primary battery by connecting to the power grid.
`Plug-in vehicle, PV`: An electric vehicle rechargeable through
wireless charging from an electric vehicle supply equipment (EVSE)
without using a physical plug or a physical socket.
`Heavy duty vehicle; H.D. Vehicle`: Any four-or more wheeled
vehicle as defined in 49 CFR 523.6 or 49 CFR 37.3 (bus).
`Light duty plug-in electric vehicle`: A three or four-wheeled
vehicle propelled by an electric motor drawing current from a
rechargeable storage battery or other energy devices for use
primarily on public streets, roads and highways and rated at less
than 4,545 kg gross vehicle weight.
`Wireless power charging system, WCS`: The system for wireless
power transfer and control between the GA and VA including
alignment and communications. This system transfers energy from the
electric supply network to the electric vehicle electromagnetically
through a two-part loosely coupled transformer.
`Wireless power transfer, WPT`: The transfer of electrical power
from the AC supply network to the electric vehicle by contactless
means.
`Utility`: A set of systems which supply electrical energy and
include a customer information system (CIS), an advanced metering
infrastructure (AMI), rates and revenue system, etc. The utility
may provide the EV with energy through rates table and discrete
events. Also, the utility may provide information about
certification on EVs, interval of power consumption measurements,
and tariff.
`Smart charging`: A system in which EVSE and/or PEV communicate
with power grid in order to optimize charging ratio or discharging
ratio of EV by reflecting capacity of the power grid or expense of
use.
`Automatic charging`: A procedure in which inductive charging is
automatically performed after a vehicle is located in a proper
position corresponding to a primary charger assembly that can
transfer power. The automatic charging may be performed after
obtaining necessary authentication and right.
`Interoperability`: A state in which component of a system
interwork with corresponding components of the system in order to
perform operations aimed by the system. Also, information
interoperability may mean capability that two or more networks,
systems, devices, applications, or components can efficiently share
and easily use information without giving inconvenience to
users.
`Inductive charging system`: A system transferring energy from a
power source to an EV through a two-part gapped core transformer in
which the two halves of the transformer, primary and secondary
coils are physically separated from one another. In the present
disclosure, the inductive charging system may correspond to an EV
power transfer system.
`Inductive coupler`: The transformer formed by the coil in the GA
Coil and the coil in the VA Coil that allows power to be
transferred with galvanic isolation.
`Inductive coupling`: Magnetic coupling between two coils. In the
present disclosure, coupling between the GA Coil and the VA
Coil.
`Ground assembly, GA`: An assembly on the infrastructure side
consisting of the GA Coil, a power/frequency conversion unit and GA
controller as well as the wiring from the grid and between each
unit, filtering circuits, housing(s) etc., necessary to function as
the power source of wireless power charging system. The GA may
include the communication elements necessary for communication
between the GA and the VA.
`Vehicle assembly, VA`: An assembly on the vehicle consisting of
the VA Coil, rectifier/power conversion unit and VA controller as
well as the wiring to the vehicle batteries and between each unit,
filtering circuits, housing(s), etc., necessary to function as the
vehicle part of a wireless power charging system. The VA may
include the communication elements necessary for communication
between the VA and the GA.
The GA may be referred to as a primary device (PD), and the VA may
be referred to as a secondary device (SD).
`Primary device`: An apparatus which provides the contactless
coupling to the secondary device. That is, the primary device may
be an apparatus external to an EV. When the EV is receiving power,
the primary device may act as the source of the power to be
transferred. The primary device may include the housing and all
covers.
`Secondary device`: An apparatus mounted on the EV which provides
the contactless coupling to the primary device. That is, the
secondary device may be installed in the EV. When the EV is
receiving power, the secondary device may transfer the power from
the primary to the EV. The secondary device may include the housing
and all covers.
`GA controller`: The portion of the GA which regulates the output
power level to the GA Coil based on information from the
vehicle.
`VA controller`: The portion of the VA that monitors specific
on-vehicle parameters during charging and initiates communication
with the GA to control output power level.
The GA controller may be referred to as a primary device
communication controller (PDCC), and the VA controller may be
referred to as an electric vehicle communication controller
(EVCC).
`Magnetic gap`: The vertical distance between the plane of the
higher of the top of the litz wire or the top of the magnetic
material in the GA Coil to the plane of the lower of the bottom of
the litz wire or the magnetic material in the VA Coil when
aligned.
`Ambient temperature`: The ground-level temperature of the air
measured at the subsystem under consideration and not in direct sun
light.
`Vehicle ground clearance`: The vertical distance between the
ground surface and the lowest part of the vehicle floor pan.
`Vehicle magnetic ground clearance`: The vertical distance between
the plane of the lower of the bottom of the litz wire or the
magnetic material in the VA Coil mounted on a vehicle to the ground
surface.
`VA Coil magnetic surface distance`: the distance between the plane
of the nearest magnetic or conducting component surface to the
lower exterior surface of the VA coil when mounted. This distance
includes any protective coverings and additional items that may be
packaged in the VA Coil enclosure.
The VA coil may be referred to as a secondary coil, a vehicle coil,
or a receive coil. Similarly, the GA coil may be referred to as a
primary coil, or a transmit coil.
`Exposed conductive component`: A conductive component of
electrical equipment (e.g. an electric vehicle) that may be touched
and which is not normally energized but which may become energized
in case of a fault.
`Hazardous live component`: A live component, which under certain
conditions can give a harmful electric shock.
`Live component`: Any conductor or conductive component intended to
be electrically energized in normal use.
`Direct contact`: Contact of persons with live components. (See IEC
61440)
`Indirect contact`: Contact of persons with exposed, conductive,
and energized components made live by an insulation failure. (See
IEC 61140)
`Alignment`: A process of finding the relative position of primary
device to secondary device and/or finding the relative position of
secondary device to primary device for the efficient power transfer
that is specified. In the present disclosure, the alignment may
direct to a fine positioning of the wireless power transfer
system.
`Pairing`: A process by which a vehicle is correlated with the
unique dedicated primary device, at which it is located and from
which the power will be transferred. The pairing may include the
process by which a VA controller and GA controller of a charging
spot are correlated. The correlation/association process may
include the process of the establishment of a relationship between
two peer communication entities.
`Command and control communication`: The communication between the
EV supply equipment and the EV exchanges information necessary to
start, control and terminate the process of WPT.
`High level communication (HLC)`: HLC is a special kind of digital
communication. HLC is necessary for additional services which are
not covered by command & control communication. The data link
of the HLC may use a power line communication (PLC), but it is not
limited.
`Low power excitation (LPE)`: LPE means a technique of activating
the primary device for the fine positioning ad pairing so that the
EV can detect the primary device, and vice versa.
The charging station may comprise at least one GA and at least one
GA controller managing the at least one GA. The GA may comprise at
least one wireless communication device. The charging station may
mean a place having at least one GA, which is installed in home,
office, public place, road, parking area, etc.
Hereinafter, preferred exemplary embodiments according to the
present disclosure will be explained in detail by referring to
accompanying figures.
FIG. 1 is a block diagram of a wireless power transfer system using
a DC-to-AC converter according to an exemplary embodiment of the
present disclosure.
Referring to FIG. 1, a wireless power transfer system 100 according
to an embodiment may comprise a GA 110 and a VA 130.
The GA 110 may comprise an alternating current to direct current
(AC-to-DC) converter 10 having a power factor correction (PFC)
function which is connected to a grid, a DC-to-AC converter 20, a
sensor 30, and a GA coil 40. The GA 110 may further comprise a GA
controller 120. The GA controller 120 may receive detected signals
D1 and D2 from the sensor 30, and output control signals S1 and S2
for controlling switches in the DC-to-DC converter 20 based on the
received detected signals D1 and D2. The GA 110 may further
comprise a DC-to-AC converter, a filter, an impedance matching
network (IMN), a resonance circuit (RC), and so on. However,
depiction of them is omitted in FIG. 1.
The VA 130 may comprise a VA coil 50 forming a coupled circuit with
the GA coil 40, an RC/IMN 60, a rectifier 70 having a filter
function, and an impedance converter 80. The impedance converter 80
may be connected to a battery 150. The VA 130 may further comprise
a VA controller 140. The VA controller 140 may be connected with an
electronic control unit 160 such as an engine control unit of the
vehicle.
During wireless power transfer, the VA controller 140 may perform
command and control communications and/or high-level communications
with the GA controller 120 via a wireless communication link.
The operation procedure of the wireless power transfer system 100
may be explained as follows.
First, a current used for charging the battery 150 is determined in
the VA 130.
Then, a power request is transferred from the VA 130 to the GA 110
via the wireless communication link.
Then, the GA 110 may recognize the power request from the VA 130,
convert power supplied from the grid to high frequency AC power
through the AC-to-DC converter 10 and the DC-to-AC converter 20,
and transfer the converted AC power to the GA coil 40.
Then, the high frequency AC power may be transferred from the GA
coil 40 to the VA coil 50 via coupling, rectified and processed in
the VA 130, and finally used to charge the battery 150.
The above-described procedure continues until the battery 150 is
fully charged and the VA 130 transmits a signal indicating
completion of the charging to the GA.
Meanwhile, performance (efficiency and output) of the wireless
power transfer system 100 may generally depend upon performance of
the DC-to-AC converter 20 which shows remarkable differences in
performance among the components of the GA 110. Also, the DC-to-AC
converter implemented as a phase-shifted full-bridge converter may
achieve high efficiency through zero voltage switching (ZVS).
However, in the wireless power transfer system applied to EV or
HEV, an error of alignment between primary and secondary pads or
tolerance of elements such as capacitors may cause a problem that
the DC-to-AC converter cannot properly perform the ZVS.
Therefore, the present embodiment may provide a DC-to-AC converter
control method and a wireless power transfer method which are
tolerant to the error of alignment between pads and the tolerance
of elements. In the proposed method, the GA controller 120 detects
a current flowing through a primary coil (i.e. GA coil) at a
specific time, and controls switching frequencies of switches in
the DC-to-AC converter 20 according to a level of the detected
current.
The DC-to-AC converter control method which will be described below
may be basically performed in the GA controller 120. However,
various implementations are not restricted thereto. For example, a
control part (controller) existing in the DC-to-AC converter 20 may
receive a signal directly from the sensor 30, and control switching
operations of the switches in the DC-to-AC converter 20. Also,
according to implementations, the DC-to-AC converter control method
may be performed, within a given control permission, by the VA
controller 140 that is connected to the GA controller 120 via a
wireless communication link. In this case, the GA controller 120
may relay command and control communications and/or high-level
communications between the VA controller 140 and the sensor 30 or
between the VA controller 140 and the DC-to-AC converter 20.
FIG. 2 is a flow chart showing a DC-to-AC converter control method
according to an exemplary embodiment of the present disclosure.
Referring to FIG. 2, in the DC-to-AC converter control method
according to an embodiment, the DC-to-AC converter may comprise
first, second, third, and fourth switches arranged in a form of a
bridge circuit between a power source and a primary coil, and may
be controller by the GA controller. Here, a first series circuit
stage of the first and third switches, and a second series circuit
stage of the fourth and second switches may be connected in
parallel for the primary coil (will be explained later referring to
FIG. 4).
First, the GA controller may detect a current flowing through the
primary coil at a rising edge of an output voltage pulse of the
DC-to-AC converter (S21).
Then, the GA controller may determine whether strength (i.e.
current level) of the detected current is at a negative level which
falls within a predetermined reference range (S22).
Then, when the current is not at the negative level which falls
within the predetermined reference range, the GA controller may
change switching frequencies (S23).
On the contrary, when the current is at the negative level which
falls within the predetermined reference range, the GA controller
may maintain current switching frequencies (S24).
According to the present embodiment, it can be prevented that the
switches of the DC-to-AC converter cannot perform ZVS due to an
error of alignment between pads comprising the primary coil and the
secondary coil, and/or tolerances of capacitor elements. Thus, a
DC-to-AC converter, which is a type of phase-shifted full-bridge
converter and is tolerant to the error of alignment and tolerances
of capacitor elements, can be provided. Especially, performance
reduction of the DC-to-AC converter, which becomes severe in
high-power transfer for EV or HEV, can be suppressed so that
reliability and stability of a wireless power transfer system can
be remarkably enhanced.
FIG. 3 is a flow chart showing a DC-to-AC converter control method
according to another exemplary embodiment of the present
disclosure.
The DC-to-AC converter control method according to another
embodiment may correspond to a more specific embodiment described
with reference to FIG. 2.
Referring to FIG. 3, the GA controller may detect a first current
at a rising edge, and a second current at a falling edge (S31). The
rising edge may correspond to a time when an output voltage pulse
of the DC-to-AC converter rises from 0V to a positive level, and
the falling edge may correspond to a time when an output voltage
pulse of the DC-to-AC converter falls from 0V to a negative level.
The rising edge and the falling edge may be referenced by a
direction from zero voltage to the positive level or the negative
level, but it is not limited.
Then, the GA controller may determine whether strength of the first
current is at a negative level below a first reference level (S32).
When the first current is at the negative level below the first
reference level, the GA controller may decrease switching
frequencies of the DC-to-AC converter (S33).
Then, the GA controller may determine whether strength of the first
current is at a positive level (S34). When the first current is at
the positive level at the rising edge, the GA controller may
increase switching frequencies of the DC-to-AC converter (S35).
Although it was explained that the step S32 is performed before the
step S34, various embodiments are not restricted thereto. That is,
the step S34 may be performed before the step S32. Alternatively,
the step S32 and the step S34 may be performed simultaneously or in
parallel.
Then, the GA controller may determine whether strength of the
second current is at a positive level over a second reference level
(S36). When the second current is at the positive level over the
second reference level at the falling edge, the GA controller may
decrease switching frequencies of the DC-to-AC converter (S37).
On the other hand, in the above-described steps S32, S34, and S36,
if the first current or the second current is not at the negative
level or the positive level, the GA controller may maintain current
switching frequencies (S38).
FIG. 4 is a block diagram of a wireless power transfer system which
can use a DC-to-AC converter control method according to
embodiments of the present disclosure.
Referring to FIG. 4, a wireless power transfer system according to
embodiments of the present disclosure may wirelessly transfer a
power of a power source 8 to a battery. For this, the wireless
power transfer system may include, as primary side components, an
AC-to-DC converter (AC rectifier) 11, a PFC converter 12, a
DC-to-AC converter 20, a sensor 30, and a primary pad 42. Also, the
wireless power transfer system may include, as secondary side
components, a secondary pad 52, and a rectifier and filter 70. The
primary pad 42 may comprise a primary coil, and the secondary pad
52 may comprise a secondary coil.
More specifically, the AC-to-DC converter 11 may comprise first to
fourth diodes D1, D2, D3, and D4 which are arranged in a form of a
bridge circuit located between the power source 8 and the PFC
converter 12. The AC-to-DC converter 11 may convert AC power (e.g.
commercial power) of the power source 8 to DC power. Although the
AC-to-DC converter 11 is configured to comprise four diodes in the
present embodiment, configuration of the AC-to-DC converter 11 is
not restricted thereto. For example, at least one of the four
diodes may be substituted with a switch having a diode
function.
The PFC converter 12 may comprise inductors, switches, diodes, and
capacitors. Also, a controller of the PFC converter 12 may convert,
by controlling operations of the switches according to a waveform
or phase of an input current or voltage, an output voltage of the
AC-to-DC converter 11 to a substantially constant voltage thereby
enhancing power efficiency. The PFC converter 12 may be classified
into a boost type, a buck type, a buck-boost type, and a resonance
type. The controller of the PFC converter 12 may be an independent
controller. However, it may be implemented using at least part of
the GA controller (refer to 120 of FIG. 1) or as a component
performing corresponding functions.
The above-described AC-to-DC converter 11 and the PFC converter 12
may correspond to the AC-to-DC converter (refer to 10 of FIG. 1),
and may also be referred to as a primary power converting part
having a PFC function.
The DC-to-AC converter 20 may be a phase-shifted full-bridge
converter. Also, the DC-to-AC converter 20 may comprise first to
fourth switches SW1, SW2, SW3, and SW4 each of which has a first
terminal, a second terminal, and a control terminal.
A first terminal of the first switch SW1 is connected with a second
terminal of the third switch SW3, and a second terminal of the
first switch SW1 and a first terminal of the third switch SW3 are
connected to both ends of the primary coil. A first terminal of the
fourth switch SW4 is connected with a second terminal of the second
switch SW2, and a second terminal of the fourth switch SW4 and a
first terminal of the second switch SW2 are also connected to both
ends of the primary coil. Also, a first connection node of the
first and third switches SW1 and SW3 and a second connection node
of the fourth and second switches SW4 and SW2 are connected to both
output ends of the PFC converter 12 or the AC-to-DC converter
11.
The output voltage V.sub.t of the DC-to-AC converter 20 may
correspond to a voltage between the first connection node and the
second connection node, and the output current I.sub.t of the
DC-to-AC converter 20 may correspond to a current flowing from the
first connection node to the primary coil. Also, when the DC-to-AC
converter 20 converts the power from the power source 8 (i.e.
power-factor-corrected DC power) to a DC power having a different
level by controlling the first to fourth switches SW1 to SW4 based
on control signals from a controller of the DC-to-AC converter 20,
according to an input voltage or an input current, a series circuit
constituted by the first and third switches SW1 and SW3 may become
a first stage, and a series circuit constituted by the fourth and
second switches SW4 and SW2 may become a second stage.
The controller of the DC-to-AC converter 20 may be an independent
controller. However, without being restricted thereto, it may be
implemented using at least part or a corresponding functional
component of the GA controller (120 of FIG. 1).
The primary pad 42 may include the primary coil (or, GA coil). The
primary pad 42 may further comprise a means for helping magnetic
field generation in the primary coil, and a means for supporting or
protecting the primary coil.
The rectifier and filter 70 may comprise a rectifier which is
connected to the secondary coil and rectifies an AC voltage induced
in the secondary coil, and a filter which is located in a back end
of the rectifier and generates a smooth DC voltage by reducing
ripples of a DC voltage obtained by the rectifier. The rectifier
and filter 70 may be connected to batteries in a battery assembly
152.
Also, according to implementations, a back end of the rectifier and
filter 70 may further comprise a regulator or an additional
converter. In this case, the battery assembly 152 may be
implemented as further including an additional converter as well as
the batteries. The additional converter may be enclosed in a single
housing together with the batteries.
According to the present embodiment, the AC commercial power may be
rectified to a positive voltage through the AC rectifier 11, and
converted to a constant DC voltage through the PFC converter 12.
The DC-to-AC converter 20, which is a phase-shifted full-bridge
converter, may convert the constant DC voltage to a high-frequency
DC voltage/current. The high-frequency DC voltage/current may be
converted to a high-frequency AC voltage/current by a DC-to-AC
converter and be transferred to the primary pad 42. Then, an AC
voltage is transferred to the secondary pad 52 inductively coupled
with the primary pad 42, and the AC voltage may be converted to a
DC voltage through the rectifier and filter 70. The secondary side
of the wireless power transfer system may use the DC voltage to
directly charge the batteries or to charge the batteries through
the additional converter.
FIG. 5 is a timing diagram of an optimal operation of a DC-to-AC
converter according to an exemplary embodiment of the present
disclosure.
Referring to FIG. 5, a DC-to-AC converter according to the present
embodiment may be a phase-shifted full-bridge converter comprising
first to fourth switches. A controller of the DC-to-AC converter
may perform ZVS in order to improve efficiency of the
converter.
An optimal operation of the DC-to-AC converter may be explained as
follows.
When the DC-to-AC converter operates, an output end of the DC-to-AC
converter may supply, to the primary coil, a current I.sub.t and a
voltage V.sub.t. The current I.sub.t may have a sine wave form with
a maximum value of about 14 A as an example, and the voltage
V.sub.t may have a pulse form with a maximum value of about 20V as
an example.
The third switch SW3 of the DC-to-AC converter may perform on-off
operations in response to a third control signal V.sub.gate3 having
a pulse form with a predetermined voltage level (e.g. 1V), and the
first switch SW1 of the DC-to-AC converter may perform on-off
operations in response to a first control signal V.sub.gate1 having
a pulse form with a predetermined voltage level (e.g. 1V). In a
time-axis, on-pulses of the third control signal and on-pulses of
the first control signal may be applied to respective switches SW3
and SW1 alternately, and they may maintain a predetermined gap from
each other.
In the above-described case, when the third switch performs on-off
operations in response to the third control signal, a current
I.sub.MOS3 of the third switch SW3 falls from 0V to a negative
level for zero-voltage switching (refer to a dotted line circle A3)
at a falling edge of a positive pulse of V.sub.t by the third
control signal, rises from the negative level to a positive level
during a period of zero and a negative pulse of V.sub.t, and falls
from the positive level to zero at a rising edge of the negative
pulse of V.sub.t by the third control signal.
Also, when the first switch SW1 performs on-off operations in
response to the first control signal, a current I.sub.MOS1 of the
first switch SW1 falls from 0V to a negative level for zero-voltage
switching (refer to a dotted line circle A1) at a rising edge of a
negative pulse of V.sub.t relating to the first control signal,
rises from the negative level to a positive level during a period
of zero and a positive pulse of V.sub.t relating to the first
control signal, and falls to 0V at a falling edge of the positive
pulse of V.sub.t. relating to the first control signal.
Similarly, the fourth switch SW4 of the DC-to-AC converter may
perform on-off operations in response to a fourth control signal
V.sub.gate4 with a pulse form having a predetermined voltage level
(e.g. 1V), and the second switch SW2 of the DC-to-AC converter may
perform on-off operations in response to a second control signal
V.sub.gate2 with a pulse form having a predetermined voltage level
(e.g. 1V). In a time-axis, on-pulses of the fourth control signal
and on-pulses of the second control signal may be applied to
respective switches SW4 and SW2 alternately, and they maintain a
predetermined gap from each other.
In the above-described case, when the fourth switch SW4 performs
on-off operations in response to the fourth control signal, a
current I.sub.MOS4 of the fourth switch SW4 from 0V falls to a
negative level which is slightly lower than 0V (e.g. by about 1V)
for zero-voltage switching (refer to a dotted line circle A4) of
the fourth switch SW4 at a falling edge of a negative pulse of
V.sub.t and a falling edge of a gate pule of the second control
signal, starts to rise from the negative level which is slightly
lower than 0V to a positive level at a rising edge of a just
following gate pulse of the fourth control signal, and pass a
positive maximum level during a period of the positive pulse of
V.sub.t, and falls to 0V at a rising edge of a next positive pulse
of V.sub.t and a falling edge of a gate pulse of the fourth control
signal.
Also, when the second switch SW2 performs on-off operations in
response to the second control signal, a current I.sub.MOS2 of the
second switch SW2 falls to a negative level which is slightly lower
than 0V (e.g. by about 1V) for zero-voltage switching (refer to a
dotted line circle A2) of the second switch SW2 at a rising edge of
a positive pulse of V.sub.t, starts to rise from the negative level
which is slightly lower than 0V to a positive level at a rising
edge of a just following gate pulse of the second control signal,
and pass a positive maximum level during a period of the positive
pulse of V.sub.t, and falls to 0V at a falling edge of a next
negative pulse of V.sub.t and a falling edge of a gate pulse of the
second control signal.
In the above-described cases, the DC-to-AC converter may perform
ZVS of all the switches through soft switching driven by a switch
driver of the controller, thereby operating as maintaining optimal
states.
However, when misalignment between the primary pad including the
primary coil and the secondary pad including the secondary coil
occurs, or manufacturing tolerances of pads or capacitors exist,
resonance may be broken while performing wireless charging. Also,
inverse-currents through switches in the converter may be generated
excessively, ZVS of the converter may not be guaranteed, and
efficiency of the wireless power transfer system may degrade.
Also, switches having large current capacity should be used in
order to cope with the inverse-currents. In addition, if the ZVS is
not guaranteed, increase of electromagnetic interference (EMI)
caused by hard switching may demand a filter for reducing the EMI,
whereby the size and material cost of the total system are
increased.
The unfavorable operational condition of the DC-to-AC converter,
the case where excessive inverse-currents flow through switches,
may be explained referring to FIG. 6. Also, the unfavorable
operational condition of the DC-to-AC converter, the case where ZVS
is not properly performed in at least one switch, may be explained
referring to FIG. 7.
FIG. 6 is a timing diagram of an operation of a DC-to-AC converter
according to a comparative example.
As illustrated in FIG. 6, currents I.sub.MOS4 and I.sub.MOS2 of the
lag stage switches (i.e. SW4 and SW2) should not fall to a negative
level which is too much lower than 0V for ZVS of the lag stage
switches.
However, when inverse currents in the lag stage switches increase,
it can be identified that the current I.sub.MOS4 of the fourth
switch SW4 in the lag stage and the current I.sub.MOS2 of the
second switch SW2 in the lag stage (refer to A4a and A2a) fall to a
negative level from 0V by more than a predetermined reference
level, similarly to the currents I.sub.MOS3 and I.sub.MOS1 of the
third and first switches SW3 and SW1 in the lead stage.
Here, the predetermined reference level may be a value which is
greater than an error range (about -1V to +1V) corresponding to 0V,
and equal to or less than about 5V. That is, the predetermined
reference level may be a value of 4V.about.6V.
According to the above comparative example, since relatively large
inverse currents flow through switches in the DC-to-AC converter,
switches having such the large capacity should be used. Also, in
the comparative example, since ZVS cannot be guaranteed, EMI
increases, and additional measures for the increased EMI should be
prepared.
FIG. 7 is a timing diagram of an operation of a DC-to-AC converter
according to another comparative example.
As illustrated in FIG. 7, for ZVS, currents I.sub.MOS3 and
I.sub.MOS2 should reach 0V alternately ahead of each other at a
falling edge of respective switches, and currents I.sub.MOS4 and
I.sub.MOS2 should reach 0V alternately ahead of each other without
falling to an excessive negative level.
However, when manufacturing tolerances of pads or capacitors exist,
the current I.sub.MOS4 of the fourth switch SW4 and the current
I.sub.MOS2 of the second switch SW2 may fall to a negative level
from zero by more than the predetermined reference level. Although
a level of the current I.sub.MOS4 of the fourth switch SW4 (refer
to A4b) and a level of the current I.sub.MOS2 of the second switch
SW2 (refer to A2b) are less than a level of the current I.sub.MOS3
of the third switch SW3 (refer to A3) and a level of the current
I.sub.MOS1 of the first switch SW1 (refer to A1), ZVS of the fourth
and second switches SW4 and SW2 is unavailable because I.sub.MOS4
and I.sub.MOS2 fall into the negative level deeper than the
predetermined reference level.
In the above-described case, since all the switches cannot perform
ZVS in the DC-to-AC converter according to the comparative example,
efficiency of the converter may degrade remarkably. That is, the
DC-to-AC converter according to the comparative example cannot
properly perform ZVS due to existence of manufacturing tolerances
of elements, and thus power or efficiency of the wireless power
system may degrade.
FIG. 8 is a timing diagram of an operation of a DC-to-AC converter
according to an exemplary embodiment of the present disclosure.
Referring to FIG. 8, a DC-to-AC converter control method according
to an embodiment of the present disclosure may resolve the
above-described problems that inverse currents flow through
switches or ZVS cannot be properly performed due to misalignment
between the primary and secondary coils and/or manufacturing
tolerances of elements.
For this, in the DC-to-AC converter control method according to an
embodiment, the following two steps are performed. First, a current
I.sub.t flowing through the primary coil may be sensed. Second,
gate pulses of lag stage switches of the DC-to-AC converter which
is a phase-shifted full-bridge converter are sensed. Here, the lag
stage may correspond to a second stage to which signals later than
signals of a first stage of the DC-to-AC converter are applied.
That is, the lag stage switches may be the fourth switch SW4 and
the second switch SW2. Also, the gate pulses may correspond to
control signals applied respectively to control terminals of the
fourth switch SW4 and the second switch SW2.
The above-described two steps can resolve the above-described
problems of the conventional DC-to-AC converter as follows.
First, a controller of the DC-to-AC converter, the GA controller,
the VA controller, or a combination of them (hereinafter,
`controller`) may detect a current (hereinafter, `a first current`)
flowing through the primary coil at the rising edge (t1) of an
output voltage of the DC-to-AC converter. Also, the controller may
detect a current (hereinafter, `a second current`) flowing through
the primary coil at the falling edge (t2) of the output voltage of
the DC-to-AC converter.
Then, the controller may decrease switching frequencies of the
DC-to-AC converter when the current I.sub.t of the primary coil has
a negative level which is excessively lower than zero by the
predetermined reference level at the rising edge t1.
Also, the controller may decrease switching frequencies of the
DC-to-AC converter when the current I.sub.t of the primary coil has
a positive level which is excessively higher than zero by the
predetermined reference level at the falling edge t2.
In the above-described case, since the current I.sub.t of the
primary coil leads the voltage V.sub.t when the DC-to-AC converter
decreases switching frequencies, inverse current flowing through
the switches may be reduced.
Meanwhile, the controller may increase switching frequencies of the
DC-to-AC converter when the current I.sub.t of the primary coil is
a positive level at the rising edge t1.
In the above-described case, since the current I.sub.t of the
primary coil lags the voltage V.sub.t when the DC-to-DC converter
increases switching frequencies, ZVS in all the switches may become
possible.
According to the present embodiment, the primary current may be
detected at rising and falling edges of the output voltage signal
according to control signals applied to the lag stage switches, and
switching frequencies may be actively varied according to a level
of the detected primary current. Thus, inverse current flowing
through switches may be reduced, and ZVS in all the switches can be
performed (refer to A3, A1, A4, and A2 of FIG. 5), whereby the
efficiency and output of the DC-to-AC converter can be enhanced and
sudden degradation in the efficiency and output under such the
unfavorable conditions can be prevented.
FIG. 9 is a graph showing an advantage of a DC-to-AC converter
control method according to an exemplary embodiment of the present
disclosure.
As described above, when the DC-to-AC converter control method
according to the present disclosure, efficiency and output of the
wireless power transfer system can be enhanced.
That is, as illustrated in (a) of FIG. 9, even when misalignment
between the primary coil (or, the primary pad in which the primary
coil is installed) and the secondary coil (or, the secondary pad in
which the secondary coil is installed) exists in forward/backward,
left/right, upward/downward, or their combinational direction, the
efficiency and output may gradually degrade without rapid
degradation when the misalignment increases.
Also, as illustrated in (b) of FIG. 9, even when elements of the
primary pad, a first capacitor connected to the primary coil of the
primary pad, the secondary pad, or a second capacitor connected to
the secondary coil of the secondary pad have manufacturing
tolerances, the efficiency and output may gradually degrade without
rapid degradation when the manufacturing tolerances increase.
A case of the combination of (a) and (b) of FIG. 9 is shown in (c)
of FIG. 9.
As described above, using the DC-to-AC converter control method
according to embodiments of the present disclosure, performance
(efficiency or output) of the wireless power transfer system can be
maintained through stable ZVS operations even when misalignment
between pads or manufacturing tolerances of elements exist. Also,
as explained referring to the comparative examples performing
unstable ZVS operations, EMI problems can be solved without using
additional filters, and thus the size and material cost of the GA
and/or VA of the wireless power transfer system can be reduced.
FIG. 10 is a block diagram to explain a structure of a controller
which can be used in a ground assembly according to an exemplary
embodiment of the present disclosure.
Referring to FIG. 10, a GA controller 120 according to an
embodiment may comprise a sensing part 122, a comparison part 124,
an adjusting part 126, and a realignment part 128. Each component
of the GA controller 120 may be explained in detail as follows.
The sensing part 122 may receive a signal from a sensor as
connected with the sensor. The sensor may detect a current or
voltage. Also, the sensing part 122 may detect the rising edge and
the falling edge in the output voltage pulse of the DC-to-AC
converter. Also, the sensing part 122 may detect the first current
flowing through the primary coil at the rising edge, and the second
current flowing through the primary coil at the falling edge.
The output voltage pulse may correspond to the output voltage of
the DC-to-AC converter, which has a form of pulse. The rising edge
may correspond to a time when the output voltage pulse rises from
zero to a positive level. The falling edge may correspond to a time
when the output voltage pulse falls from zero to a negative
level.
The above-described sensing part 122 may include an
analog-to-digital converter (ADC) outputting a digitalized value
indicating strength or amount of an analog value sensed by the
sensor.
The comparison part 124 may output a first comparison result when
the first current is a negative level lower than a preconfigured
first reference level at first rising edge. Also, the comparison
part 124 may output a second comparison result when the first
current is a positive level at the rising edge. Also, the
comparison part 124 may output a third comparison result when the
second current is a positive level higher than a preconfigured
second reference level at the falling edge.
Also, the comparison part 124 may compare a current output of the
wireless power transfer system with a preconfigured reference
output.
The comparison part 124 may be implemented as an integrated circuit
or as including an operational amplifier.
The adjusting part 126 may comprise a first adjusting part 126a and
a second adjusting part 126b. The first adjusting part 126a may
comprise a means for decreasing switching frequencies of the
DC-to-AC converter, or a component performing a corresponding
function, according to the comparison result of the comparison part
124. Similarly, the second adjusting part 126b may comprise a means
for increasing switching frequencies of the DC-to-AC converter, or
a component performing a corresponding function, according to the
comparison result of the comparison part 124.
The adjusting part 126 may be implemented as including switch
drivers controlling on-off operations of at least four switches in
the DC-to-AC converter.
The realignment part 128 may realign the primary and secondary pads
when the detected current output of the system is less than the
preconfigured reference output. The realignment part 128 may
transfer signals or information needed for the realignment to the
GA controller and/or VA controller. In this case, the GA controller
and/or VA controller may perform alignment between the pads again
by moving at least one of the primary and secondary pads, according
to a realignment request (i.e. the signals and information) from
the realignment part 128, to a forward, backward, left, right,
upward, downward, or their combinational direction.
The realignment part 128 may comprise a means for generating the
realignment request including realignment information and
transferring the realignment request to the GA controller and/or VA
controller, or a component performing a corresponding function.
Also, the realignment part 128 may be implemented as a means or
component performing command and control communications directly
with an actuator connected to the primary pad or the secondary
pad.
On the other hand, the controller implementing the DC-to-AC
converter control methods according to embodiments of the present
disclosure is not restricted to the above-described structure of GA
controller. That is, the above-described functional components may
also be implemented as included in the controller in the DC-to-AC
converter, or may also be implanted as included in the VA
controller connected wirelessly with the GA controller 120.
FIG. 11 is a flow chart showing a wireless power transfer method
using a ground assembly of FIG. 10.
Referring to FIG. 11, the wireless power transfer method according
to the present embodiment may be performed by a GA. However,
according to implementations, the wireless power transfer method
according to the present embodiment may be performed by a VA
controller connected to a GA controller via a wireless
communication link, a VA in which the VA controller is included, or
an electronic control unit in the vehicle.
First, the GA controller of the VA or the controller of the
DC-to-AC converter may detect a first current flowing through the
primary coil at a rising edge of an output voltage pulse of the
DC-to-AC converter (S111).
Then, the controller may determine whether the first current has a
negative level lower than a reference level (S112). When the first
current has a negative level lower than the reference level, the
controller may decrease switching frequencies of the DC-to-AC
converter (S113).
Then, the controller may detect a second current flowing through
the primary coil at a falling edge of the output voltage pulse of
the DC-to-AC converter (S114).
Then, the controller may determine whether the second current has a
positive level (S115). When the second current has a positive
level, the controller may further decrease switching frequencies of
the DC-to-AC converter (S116).
Then, the controller may determine whether a first current has a
positive level at a new rising edge following the falling edge
(S117). The step S117 may be performed when the second current is
not at a positive level in the step S115. However, various
embodiments are not restricted thereto. Also, the controller may
increase switching frequencies of the DC-to-AC converter when the
first current has a positive level at the new rising edge
(S118).
Then, the controller may determine whether a current output of the
wireless power transfer system is less than a value obtained by
subtracting a predetermined threshold from a rated output of the
system (S119). The step S119 is performed for detecting a case in
which performance degrades excessively although suppression of
system performance degradation due to misalignment between the pads
or manufacturing tolerances of elements is attempted through the
above-described procedures.
After the step S119, when the current output of the wireless power
transfer system is less than the value (i.e. rate
output--predetermined threshold), the wireless power transfer may
be stopped and alignment between the primary and secondary coils
may be performed again (S120). On the contrary, when the current
output of the system is equal to or larger than the value, the
basic process of the wireless power transfer according to
embodiments of the present disclosure may be maintained or
resumed.
According to the above-described embodiments, even when
misalignment between the primary coil and the secondary coil exists
in forward/backward, left/right, upward/downward, or their
combinational direction, rapid degradation in the efficiency and
output of the system can be prevented. Also, the wireless power
transfer procedure can be effectively managed, if necessary,
through realignment of the pads.
While the exemplary embodiments of the present disclosure and their
advantages have been described in detail, it should be understood
that various changes, substitutions and alterations may be made
herein without departing from the scope of the disclosure.
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